Jeofizikkulubu | Geophysics

Jeofizikkulubu | Geophysics

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Astrobiologist Dale Andersen Antarctic Status Report 20 November 2017: Preparing Diving Gear
Dale Andersen sent this message from: Lat -71.33293 Lon 13.45381 on 20 November 2017 5:22:14 AM EST: "Hi Keith: Looks like our weather is improving,...
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An integrated approach for extraction of lithology information using the SPOT 6 imagery in a heavily Quaternary-covered region—North Baoji District of China
We studied the applicability of SPOT (Systeme Probatoire d'Observation de la Terre) 6 satellite imagery for red sandstone interpretation in the heavily loess-covered northern Baoji...
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New Delhi smog, death-sentence appeal and a porpoise setback
The week in science: 11–16 November 2017.
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Astrobiologist Dale Andersen Antarctic Status Report 19 November 2017: Bad Weather
Dale Andersen sent this message from: Lat -71.33293 Lon 13.45381 on 19 November 2017 at 1:43:18 AM EST: "The weather here is pretty bad with...
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Astrobiologist Dale Andersen Antarctic Status Report 20 November 2017: Preparing Diving Gear
Dale Andersen sent this message from: Lat -71.33293 Lon 13.45381 on 20 November 2017 5:22:14 AM EST: "Hi Keith: Looks like our weather is improving,...
Read More
An integrated approach for extraction of lithology information using the SPOT 6 imagery in a heavily Quaternary-covered region—North Baoji District of China
We studied the applicability of SPOT (Systeme Probatoire d'Observation de la Terre) 6 satellite imagery for red sandstone interpretation in the heavily loess-covered northern Baoji...
Read More
New Delhi smog, death-sentence appeal and a porpoise setback
The week in science: 11–16 November 2017.
Read More
Astrobiologist Dale Andersen Antarctic Status Report 19 November 2017: Bad Weather
Dale Andersen sent this message from: Lat -71.33293 Lon 13.45381 on 19 November 2017 at 1:43:18 AM EST: "The weather here is pretty bad with...
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Immunization needs a technology boost
Tracking who receives vaccines is essential, but will be impossible without innovations in digital technologies, says Seth Berkley.
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How China could make the most of its beamlines
More international collaboration could build capacity at big physics facilities especially in the south.
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RED Engineering sees ‘strong opportunities’ for growth in 2018 on the back of innovative engineering solutions
UK engineering services firm RED Engineering sees ‘strong opportunities’ in the offshore oil and gas sector for firms with capacity to deliver innovative fast track...
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Women in Energy Conference Highlights Growing Role of Women in Oil and Gas Workforce
Event Held as Part of ADIPEC 2017, Empowering a New Generation of Female Professionals to Break the Glass Ceiling Career Opportunities Needed for Science, Technology...
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Petrogenesis and tectonic setting of Carboniferous hornblende gabbros of the northern Great Xing’an Range, NE China: Constraints from geochronology, geochemistry, mineral chemistry, and zircon Hf isotopes

This study presents new information on the petrogenesis and tectonic setting of a hornblende gabbro in the northern Great Xing’an Range of northeastern China using new whole-rock geochemical, mineral geochemical, and in situ zircon U–Pb and Hf isotopic data obtained for samples taken from near the town of Tayuan. Zircon U–Pb dating indicates that the hornblende gabbro was emplaced during the late Carboniferous (~311 Ma). The hornblende gabbros are alkaline with high K2O + Na2O (4.25–6.42 wt.%), low SiO2 (41.69–50.22 wt.%), and variable MgO (4.49–7.16 wt.%) and TiO2 (1.23–2.77 wt.%) contents. The pressure and temperature conditions of gabbro crystallization were determined using amphibole–plagioclase and amphibole thermobarometry, which indicate that the Tayuan hornblende gabbro formed at pressures of 4.1–6.9 kbar and temperatures of 686–762 °C, respectively. The hornblende gabbros are enriched in light rare earth elements and large ion lithophile elements, are depleted in the heavy rare earth elements and high field strength elements, and have positive zircon εHf(t) values (+3.9 to +9.9), all of which are indicative of formation from magmas generated by the partial melting of a depleted region of the lithospheric mantle that was previously metasomatized by subducted slab-derived fluids and/or melts just before the generation of the hornblende gabbro magmas. The field observational, geochronological, geochemical, mineral geochemical, and zircon Hf isotopic data presented here are indicative of a complex petrogenetic history that involved crystal fractionation and magma mixing. These hornblende gabbros were emplaced in an extensional setting associated with the collision of the Xing’an and Songnen massifs.

Dynamic mechanism of tectonic inversion and implications for oil–gas accumulation in the Xihu Sag, East China Sea Shelf Basin: Insights from numerical modelling

The East China Sea Shelf Basin (ECSSB) lies at the south-eastern margin of the Eurasian Plate and was affected by the subduction of the Pacific Plate and the Philippine Plate. It experienced and recorded multistage tectonic inversions in the Cenozoic, especially in the Xihu Sag. In an attempt to investigate the evolution and mechanism of tectonic inversion, this paper presents numerical simulation results by the finite element method to the Xihu Sag. Combined with comprehensive structural analyses of seismic profiles, this paper determines the structural geometry of the sag for establishing a viscoelastic geologic model including six-layer strata and nine major faults. Simulation results show that the boundary conditions of transtension and transpression control the inversion process that propagates from east to west, and the distribution of low compressive stress displays certain correlations with the distribution of oil deposits. Based on quantitative analysis of the vertical displacement field of the Xihu Sag, this paper identifies a tectonic inversion process, which indicates that the western part of the sag uplifts and the eastern part subsides during the first-stage inversion; whereas the western part subsides and central-eastern parts uplift during the second and third stages. The formation of the tectonic inversion is controlled by the adjustment of the stress field from dextral transtension to sinistral transpression caused by the change of subduction rates and direction of the Pacific Plate and the Philippine Sea Plate.

Origin and Palaeozoic reworking of the Central Tianshan Block, southern CAOB: Constraints from provenance analysis of metasedimentary rocks in northern Xinjiang Province and adjacent region

There are several Precambrian microcontinents in the Central Asian Orogenic Belt (CAOB). Across these microcontinents, there are many metasedimentary rocks which were not all deposited in the Precambrian. We report on a field-based petrological and zircon geochronological study of metasedimentary rocks from the Tianshan and Beishan orogens, southern CAOB, in order to reveal the Precambrian affinity and Palaeozoic reworking. Most metasedimentary rocks in the Central Tianshan Block (CTB) and Dunhuang arc accretionary system reveal Palaeozoic records of arc accretion, collision, and postcollisional processes. The zircon age patterns of these metasedimentary rocks in the CTB show strong affinity to the Tarim Craton, whereas those of the Dunhuang arc accretionary system suggest a Mongolian affinity. The CTB constituted an independent microcontinent during the Palaeozoic accretionary process and was transformed into a Japan-type arc until it became amalgamated with the Tarim Block in the late Permian. In contrast, the Dunhuang Block shows a probable Mongolian affinity and was a stable unit during the late Mesoproterozoic to Neoproterozoic until the beginning of CAOB orogenesis.

Petrogenesis of the Jurassic adakitic rocks in Gan-Hang Belt South China: Response to the Palaeo-Pacific Plate oblique subduction

To explain the roughly contemporary magmatic activities between Cathaysia Block and both sides of the Jiangnan Orogenic Belt, we discussed the magmatic-ore related and closely compressive tectonism in the Gan-Hang Belt. Also, we compared the Yongping Pluton and Yinshan volcanic-plutonic rocks in northeastern Jiangxi, and Huangshitan and other plutons in the northern Zhejiang, which were produced in the setting of compressive tectonism. We compared bimodel dikes and Sanqingshan A-type granite in the northeastern Jiangxi, and Huanshitan and other A-type granites in the northern Zhejiang, which formed in the setting of extension. We proposed that approximately in Middle Jurassic time (175 ± 5 Ma), South China entered into the tectonic system, roughly from south to north oblique subduction of the Paleo-Pacific Plate. The intermission period of the magmatic activities in Japan and South Korea (~170–120 Ma) was actually the period of the large-scale magmatic-ore forming activities in South China. Thus, this oblique subduction resulted in the dynamic imbalance and mutual movement from the deep part to the shallow part of the crust among surrounding blocks of South China and the multiple blocks of South China including those orogens between the North and South China blocks, between the Yangtze Craton and Cathayasian Block, and between the South China Block and Indosinian Block, as well as microcontinental blocks within Cathaysia Block. At present, we cannot rule out the influence of compressional–extensional tectonism for the Gan-Hang Belt controlled by the Paleo-Asia tectonic system.

Ore genesis of the Xiadian gold deposit, Jiaodong Peninsula, East China: Information from fluid inclusions and mineralization

Orebodies in the Xiadian gold deposit in the Jiaodong Peninsula, China are mainly hosted in the Mesozoic granitoids, controlled structurally by the Zhaoyuan–Pingdu Fault Zone, and occur as disseminated and cataclastic altered type. Four mineralization stages were identified as follows: quartz–pyrite stage (I), gold-bearing fine-grained pyrite–quartz stage (II), polymetallic sulfide–quartz stage (III), and quartz–carbonate stage (IV). Quartz was classified as including quartz granules with dentation boundaries (I), cataclastic quartz grain assemblages (II and III), and rod-like quartz grains (IV). Petrography, laser Raman analysis, and microthermometry of fluid inclusions in these stages (in both tunnel and borehole samples) reveal (a) CO2–H2O fluid inclusions (C–H type), (b) CO2–H2O ± CH4 fluid inclusions (C–H–CH4 type), and (c) aqueous fluid inclusions (H type). Fluid immiscibility caused by fluid mixing caused rapid precipitation of gold. The ore-forming fluid of the Xiadian gold deposit evolves from an H2O–CO2–NaCl ± CH4 system with medium temperature and salinity to an H2O–NaCl system with low temperature and salinity, from CO2-rich to CO2-poor in composition and from a mixture of magmatic water with increasing meteoric water as δ18OH2O values. Sulphur isotope compositions suggest a mixed source of ore metal, and the Jiaodong Group may be a major source for sulphur. Fluid parameters of borehole samples indicate that there is the same fluid system for Au precipitation at different depths and fault gouge with poor permeability may play a crucial role in forming a relatively closed semi-open space for Au precipitation. Integrating the data obtained from the studies including regional geology, ore geology, and fluid inclusions and stable isotope geochemistry, the Xiadian gold deposit is concluded as an orogenic-type gold deposit formed in the tectonic transition from compression to extension.

Late Triassic Dabie–Sulu Orocline: New exhumation model of the HP–UHP rocks

The Dabie–Sulu orogen is located in the eastern segment of the Central China Orogen between the North China Block (NCB) and the South China Block (SCB). The complex processes of break-up and assemblage among the continental blocks of East Asia caused them to undergo multiple-stage continental collisions. It is extremely important for the final kinematics and dynamics of convergence and collision among continental blocks to explore the exhumation mechanism of the HP (high pressure)-UHP (ultra-high pressure) metamorphic rocks. Therefore, this paper focuses on the final collisional process and tries to find a reasonable exhumation mechanism of the HP–UHP rocks. On the basis of the structural geology, petrology, seismic tomography, palaeomagnetism, and mathematical calculation, we propose a south-eastward subduction of the NCB under the SCB in the Indosinian, and the Sulu Orogen actually became an orocline. This was caused by continuous south-eastward subduction and the subsequent westward-retreating delamination of the NCB slab. Coevally, it produced a two-stage exhumation process, a vertical extrusion during the first stage (240–220 Ma) and an eastward extrusion controlled by an oroclinal contraction at the second stage (220–200 Ma).